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From: christian.bau@cbau.wanadoo.co.uk
Newsgroups: comp.compilers
Subject: Re: Compiler optimization and floating point operations
Date: Mon, 28 Oct 2013 15:54:46 -0700 (PDT)
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On Thursday, October 24, 2013 5:38:13 PM UTC+1, Steven G. Kargl wrote:
> #include <stdio.h>
> int
> main(void)
> {
>    float a, b;
>    a = 0.;
>    b = a / a;
>    if (a + b != b + a) printf("fubar\n");
>    return (0);
> }
>
> Can an optimizing compiler eliminate the if-statement?

It can eliminate the test because it will always be true (on IEEE
implementations where 0.0 / 0.0 is NaN).  It cannot eliminate the
if-statement because printf () should be called.